IP addresses added via Plesk are gone from the interface but are listed in plesk

Symptoms

Debian 9 on OVH infrastructure is used.

The /etc/systemd/network/50-default.network exists with the following text at the beginning:

# cat /etc/systemd/network/50-default.network# This file sets the IP configuration of the primary (public) network device.# You can also see this as "OSI Layer 3" config.# It was created by the OVH installer, please be careful with modifications.